A is correct. The question is what layers it's working on and the answer is from the lower layers up to and including application layer(all layers).
If you tink D is correct maybe you misunderstood the question?
It's not asking if Application layer is upper level or lower level.
A is Correct
The concept of Application Firewall is very well explained in CCSA book page 26.
"Application Layer Firewalls inspect traffic through the lower layers of the TCP/IP model and up to and including the Application layer. They are usually implemented through software running on a host or stand-alone network hardware and are used in conjunction with Packet Filtering"
TCP/IP model has 4 layers (Top to bottom) unlike OSI 7 layers.
Application
Transport
Internet
Network access
I think the current answer is worng. Any suggestions, guys?
The lower layer includes the internet layer. so upper layer inspection begins only after the packet filtering (src/dest/service/action) so the answer is correct.
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